1. Field of Invention
In an electronic control system for an automatic transmission, a solenoid is controlled by a pulse signal output based on an analog signal from a sensor. The invention relates to a vehicular input signal detecting system which is structured so that the sampling of the analog signal from the sensor is timed with the pulse signal output to control the solenoid so that the fluctuation of the pulse signal does not influence the sensor output. This method results in an accurate and stable signal.
2. Description of Related Art
In an electronic control system of an automatic transmission of the prior art, as shown in FIG. 8, an analog input, such as the throttle opening or a vehicle speed, is input from each sensor S at a predetermined sampling period, converted to digital data by A/D input processing, and compared to data stored in a memory of a CPU to identify an output voltage for application to a linear solenoid L for shifting control.
In this control system, noise from the pulse-width-modulated (PWM) output voltage applied to the linear solenoid L causes fluctuation in the voltage waveform of the analog input of each sensor S.
Moreover, for the detection of the vehicle input signal of the prior art, filter processing is executed without any synchronization with the PWM output period. As a result, an accurate and stable input of each sensor S cannot be detected because of the fluctuation in the voltage waveform of the analog input according to the period of the PWM output.